Field of the Invention
This invention relates to a control system for pulse width modulation-operated (PWM signals) solenoid valves comprising a seal seat, a valving or sealing member, elastic means operating on said valving member to tend to maintain said member on the seal seat, and a solenoid which, when energized, withdraws the valving member from the seal seat against the action of the elastic means.
The system is of the type in which the valve opening pulses are provided by a microcontroller or the like, which amplitude-modulates the width of said pulses on the basis of the user-set flow rate of the fluid (generally fuel gas) passing through the valve.
At that end intended to cooperate with the seal seat, the sealing member comprises an elastomer part. When the solenoid is de-energized, the spring violently urges the sealing member against the relative seat. During this stage the elastomer part hence absorbs all the kinetic energy possessed by the relative sealing member following the thrust of the spring, the impact against the seal seat being such as to produce permanent deformation of the elastomer material with the passage of time, so limiting the useful life of the solenoid valve, especially when frequent switching is necessary, as in the case of control by PWM signals.
Description of the Related Art
Italian patent application MI95A001856 filed on Jan. 9, 1995 in the name of the present applicant describes a system for remedying this problem. According to this known system a force counteracting the spring is applied to the valving member when moving towards the seal seat, to reduce the impact energy between the relative sealing member and the relative seat. According to this known system, a feedback circuit is provided which carries the information relative to the start of the actuator movement to a microprocessor to operate the braking force.
This known system eliminates (or reduces) the effect of the impact against the seat, but includes the use of a suitable feedback circuit. However it does not also allow the valving member to be damped during the opening stage, with consequent annoying noise when this member collides on termination of opening, together with vibration and hence noise induced in the structures connected to the valve, and lack of perfect linearization of flow control (ie the flow does not increase linearly with increased duty cycle).